A Highly Sensitive Flexible Electrochemical Sensor via Fe−C@Fe/Ce−C Bilayer Heterojunction with a Built-in Electric Field for H ₂ O ₂ Detection

Hydrogen peroxide (H 2 O 2 ), a key reactive oxygen species in physiological and pathological processes, demands highly sensitive detection for biological and biomedical research, yet developing electrocatalytic materials with high sensitivity, low detection limit, and excellent stability remains a challenge. Herein, a Fe−C@Fe/Ce−C bilayer heterojunction composite was fabricated for H 2 O 2 detection. Benefiting from its unique heterojunction architecture and synergistic Fe/Ce/carbon interactions, the as-prepared nanocomposite exhibits the exceptional H 2 O 2 sensing performance, with a wide linear range of 0.5−6000 µM, a high sensitivity of 490.5 μA·mM −1 ·cm −2, a low detection limit of 0.12 µM, excellent anti-interference selectivity against common biological interferents, and outstanding long-term stability with no obvious performance variation after 11 days of continuous testing. The robust built-in electric field arising from the heterojunction facilitates interfacial charge transfer and accelerates H 2 O 2 activation, boosting sensing behavior. Furthermore, the flexible electrochemical sensor was fabricated via the screen-printing technology, which enables reliable real-time monitoring of intracellular H 2 O 2 released from HeLa cells, showing great potential for biological sensing. This work provides a promising design strategy for high-performance flexible electrochemical sensors and deepens the understanding of heterojunction and built-in electric field roles in electrocatalytic sensing systems.